Electronic and optical systems typically include a variety of electronic or optical components assembled on a substrate. For example, integrated circuits, resistors, capacitors, discrete transistors, inductors, voltage regulators, and electrical connectors are often mounted together on printed-circuit boards. As electronic and optical systems become smaller and more highly integrated, ever-smaller components must be assembled on substrates. For example, surface mount components as small as 400 microns in length can be assembled on circuit boards using pick-and-place equipment.
Even smaller micro-devices having dimensions less than 100 microns can be assembled using, for example, micro-transfer printing techniques. For example, U.S. Pat. No. 8,722,458 describes transferring light-emitting, light-sensing, or light-collecting semiconductor elements from a wafer substrate to a destination substrate using a patterned elastomer stamp whose spatial pattern matches the location of the semiconductor elements on the wafer substrate. In certain embodiments of micro-transfer printing, small integrated circuit chips or chiplets are typically natively formed on a silicon substrate using photolithographic processes. The silicon substrate facilitates the formation of anchors on the wafer and tethers between the wafer and the chiplet that are broken during the micro-transfer printing process.
Micro-transfer printing can be used with a wide variety of component types in a wide variety of electronic and optical system, including processors, sensors, and energy emitters such as light-emitting diodes (LEDs). For example, CMOS devices are typically formed in silicon wafers, high-power transistors are often made using compound semiconductors such as gallium arsenide, and light-emitting devices such as light-emitting diodes are constructed in doped compound semiconductors such as gallium nitride, gallium phosphide, or gallium arsenide. These various components require a corresponding variety of materials and processing methods for making transfer printable devices that can be directly transfer printed from a native source substrate or wafer to a destination substrate. Devices that are not directly micro-transfer printed from a native wafer are typically bonded to a handle wafer (for example as taught in U.S. Pat. No. 8,934,259) or transferred using two stamp transfer steps (for example as taught in U.S. Pat. No. 8,889,485).
Electronic and optical components are usually constructed on wafers using photolithography. Different wafer materials are adapted for different device types, for example silicon wafers are used to make digital integrated circuits and sapphire or SiC substrates are commonly used with light-emitting diodes, for example. Devices can be singulated from their native substrate, for example by dicing the wafer. Alternatively, devices such as light-emitting diodes (LEDs) are removed from their native substrate by laser lift off, for example as described in Large-area laser-lift-off processing in microelectronics, by Delmdahl et al in Physics Procedia 41 (2013) pp. 241-248. This work describes UV laser lift-off delamination using 248 nm excimer laser sources to remove GaN LEDs from sapphire substrates. However, these methods do not provide wafers with transfer printable micro-devices.
There is a need, therefore, for methods and materials for constructing transfer printable devices on a variety of wafer types.